This invention relates to the construction of a magnetoresistance (hereinbelow abbreviated to MR) type magnetic head and in particular to a shunt bias type MR head suitable for a high density recording devices.
The construction of prior art shunt bias type MR heads is disclosed in U.S. Pat. Nos. 3,814,863 and 3,813,692. The construction is shown in FIG. 7. According to the prior art techniques, an MR film 5 having a desired form made of Permalloy, etc. and a shunt film 4 made of titanium, molybdenum, etc. are superposed through an insulating film 2 made of e.g. alumina serving as a first head gap on a ferrite substrate 1 serving as a shield at the rear portion of these elements are disposed bonding pads 15 for connecting the exterior of the head with leads. The head is so constructed that another insulating film 6 made of e.g. alumina, etc. serving as a second head gap is formed on this ferrite substrate 1 and a ferrite plate 7 serving as a shield is adhered thereto. In the MR head constructed as described above, the height i of the ferrite plate 7 should be as great as possible so that it has a shield effect sufficient for the MR head not to sense the unnecessary part of the leakage flux from the recording medium. Moreover the reliability of the adhesion is increased by enlarging the area of the adhesion in order to increase the adhesion strength. Consequently, the distance l from the extremity of the element to the bonding pads 15 is large. For this reason, the resistance of a signal extracting part or electrical leads is great and the DC resistance of the overall element is also great. Therefore, when detection current flows through the element described above, the amount of produced heat is increased by that corresponding to the increase of the resistance of the element. Further, there is another problem that, when the amount of produced heat increases, thermal noise is also increased and the signal to noise (S/N) ratio is lowered.
As a method for solving the problem stated above, a construction is conceivable by which a conductor having a low resistivity is extended to the extremity of the MR element. U.S. Pat. No. 4,024,489 has proposed this construction. The construction proposed thereby is shown in FIGS. 8A and 8B. FIG. 8A indicates a perspective view of this construction and FIG. 8B indicates a side view of the element indicated in FIG. 8A, seen along the arrow A. The resistance of the signal extracting part s lowered to be negligibly small by forming a signal leadout conductor 3 having a low resistivity extending from the bonding pad portion to the extremity of the element, as indicated in FIG. 8A, and thus, the problem stated above can be resolved. However, when the ferrite plate 7 is adhered, a crevice B having a thickness corresponding to that of the signal leadout conductor 3 is produced between the shunt film 4 and the insulating film 6 at the extremity portion of the element by forming the signal leadout conductor 3, as indicated in FIG. 8B.
Since the length of the second gap of the shield type MR head is the interval between the MR film 5 and the ferrite plate 7, in such a structure the length of the second gap is determined by the sum of the thickness of the shunt film 4, that of the signal leadout conductor 3 corresponding to the crevice B and that of the insulating film 6. Thus, it can be understood that it is a structure which is not suitable for narrowing the second gap by the fact that it gives rise to the crevice B. Further, in the case where the ferrite substrate 1, on which the insulating film 2, the MR film 5, the shunt film 4 and the signal leadout conductor 3 are formed, is connected with a ferrite plate 7, on which the insulating film 6 is formed, by using an adhesive, etc., unless the adhesive is sufficiently hard with respect to the shunt film 4, when the surface of the MR head is finished by lapping, etc., the shunt film 4 is deformed so that a part thereof bites the adhesive injected into the crevice B due to working stress, etc. Since this gives rise to unevenness in characteristics of the head, sufficient attention should be paid to the selection of the adhesive.
As stated previously, for the prior art shunt bias type MR head, in the example indicated in FIG. 7, since it is necessary that l should be long for the reason described above, the resistance of the overall MR head is great and the amount of produced heat is increased by making the detection current flow therethrough. This causes a problem to increase thermal noise. On the other hand, in the example indicated in FIGS. 8A and 8B, in which the signal leadout conductor 3 is formed in order to solve this problem, there are other problems that the spacing B is produced between the shunt film 4 and the insulating film 6, and that it is difficult to reduce the length of the second gap of the shield type MR head.